Measurement of natural neutron background using electrochemically etched polycarbonate foils and boron-10 radiators

Electrochemical etching of polycarbonate foils was performed using a KOH solution with various concentrations of ethyl alcohol under different conditions of field strength, frequency, temperature and etching time to register alpha-particles from a 10B radiator positioned in the center of a 25-cm diameter polyethylene sphere. These studies showed that the highest neutron sensitivity relative to the inherent background in the foil was obtained under the following etching conditions: 32 kV/cm, 1 kHz, 30 degrees C, 2 hr in a solution of 35 gm KOH + 25 cm3 C2H5OH + 75 cm3 H20. Under these conditions, 1 mrem of neutrons from a Ra-Be source gave 155 pits per cm2 while background was 1-3 pits per cm2. The pit diameters were about 75 microns. The dose can be measured to an uncertainty of +/- 100% at 0.1 mrem and +/- 10% at 1 mrem. This method was used to measure the natural neutron background and gave 17 pits per cm2 (0.1 mrem +/- 0.1 mrem) per month in a building.